A 15 minute movie is unlikely to run to 4GB, if that limit exists - I rather hope it doesn't as I converted from FAT32 to NTFS precisely to avoid such file size limitations. I have had similar problems in rendering in Pinnacle 8 (and so have others according to the Video mags), but have resolved matters by (1) installing XP clean, (2) having a dedicated second drive for video editing and (3) upgrading to 8.10 (I think) via the Pinnacle website. Now all works fine. I believe others that have had problems have overcome them by rendering an .avi file in Pinnacle and then writing to DVD via Nero or similar - this seemed such a long way around that I tried the above first.
Don't forget that rendering/writing a movie, is just about the most tortuous task you can ask of your PC. It might help to shut down all the clutter running in the background, and anything else you can think of to reduce the load. If the rendering fails at a particular point in the movie each time, try deleting the scene at which it is failing and see if it's actually the files that it's working with that are causing the problem - if it is, it will run beyond that point before completing (or failing somewhere else!!!).